The invention relates to a method for treating at elevated temperatures materials made of organic substances in the form of rubber, plastic and/or lacquers or provided with organic substances in the form of rubber, plastics or lacquers.
In the private as well as the industrial area, enormous wastes are produced of rubber, plastics and lacquers or components provided with these substances, which in whole or in part must be considered valuable substances and should be recycled. The recycling is becoming increasingly important for ecological reasons. The processes known heretofore are incineration and vacuum distillation. Neither process is free of problems, since some chlorine and sulfur compounds are released. Some of the rubber wastes contain metals provided with anticorrosives (zinc, for example) which are oxidized and issue in the form of air-borne dust. In incineration processes very large amounts of air are used, which has to be cleaned in large gas and dust filters.
It is known to use surplus old rubber tires, i.e., tires which can no longer be recapped, as fuel in cement kilns. In this case, however, nearly all the valuable substances are lost.
In an article by Theerkorn et al., entitled "Sauberer Wirbel," published in "Maschinenmarkt," Wuburg 98 (1992), pages 30 to 35, a disclosure is made of a method for cleaning metal parts by a reductive fluidbed process in aluminum oxide powder in the presence of nitrogen and hydrogen at temperatures between 350.degree. and 1000.degree. C., but preferably above 450.degree. C. However, in addition to the metal parts gaseous substances are produced due to cracking and have to be cleaned and burned. It is even proposed to pass the waste gases through a second fluid bed at a higher temperature in order to comply with laws governing emissions. Temperatures of 950.degree. C. are even mentioned for the prevention of dioxins and furans. Gasentrained aluminum oxide particles have to be captured in a centrifugal air separator. Degreasing is performed at temperatures between 350.degree. and 460.degree. C., and between 450.degree. and 550.degree. C. if the contamination is severe, for periods of time up to 60 minutes. Many parts, especially those made of aluminum alloys, do not withstand such thermal stress. Thin-walled pieces tend to warp.
It is furthermore known to perform the degreasing and stripping of components in a reactive low-pressure plasma excited by microwaves. This apparatus, however, is expensive, and the process involves great heat stress on the components.
It is furthermore known to strip metal parts of elastomers and other plastics by cryogenic methods by chilling the objects in liquid nitrogen to -196.degree. C. thereby embrittling the plastics. The plastics that fall or are knocked off, however, have to be subjected to further processing.
No attention has been given to recycling processes for numerous valuable materials. For example, universal or CV joints on motor vehicles are guarded against dirt and dust by rubber-elastic bellows. These bellows serve a dual purpose in operation. First, they are a reservoir containing lubricant for the joint, and secondly they prevent the entry of water and abrasive dirt.
After a limited time of operation these bellows have to be replaced due to aging or also due to damage. This is done nearly always when the universal joint is replaced. The worn-out bellows are designated as problem trash. These bellows also turn up in car recycling operations with other components, such as oil seals, cap seals, O-rings or other seals.
Recycling or even disposal would be possible if the plastic or rubber were separated from the lubricants. Such separation has heretofore been accomplished by washing processes. Another method for the degreasing and deoiling of components containing plastic or rubber is the thermal vaporizing of the greases in a vacuum.
A process for this purpose is described in U.S. application Ser. No. 08/221,184, which describes a method for the degreasing and cleaning of material bearing grease and/or oily substances. According to this process the material to be cleaned is heated under vacuum conditions in a process chamber such that the greases and/or oils can be separated from the material according to their physical condition.
For any further use of the rubber parts thus degreased they have to be chopped up and ground. The grinding process is far more difficult than the degreasing, but it can be performed by freezing, with liquid nitrogen for example.
These known methods and apparatus have the disadvantage that, for example, even after combustion large amounts of solid and gaseous wastes are produced, which have to be disposed of separately or released to the atmosphere by burning. The gases released by combustion contain large amounts of metal oxides (e.g., oxides of zinc, cadmium, vanadium, arsenic etc.), some of which are highly toxic.